The invention relates to a cutting device for crop material.
The invention furthermore relates to a method for adjusting the shear bar of a cutting device.
Agricultural harvesting machines such as forage harvesters in particular comprise a cutting device having a cutting tool in the form of a cutting cylinder which rotates relative to a stationary shear bar. Crop that reaches an engagement region formed by the rotating cutting cylinder and the shear bar is fragmentized, being chopped in particular, by the interaction of cutting blades—which are attached to the rotating cutting cylinder—with the shear bar. The cutting cylinder is therefore also referred to as the chopper drum.
The cutting blades become worn during operation. They are therefore sharpened repeatedly, in order to attain a consistent cutting quality and minimize the cutting forces and, therefore, the drive energy required for chopping.
Every time sharpening is performed, material is removed from the cutting blades when the blunt cutting edges are sharpened. The distance between the shear bar and the cutting edges of the cutting blades attached to the cutting cylinder is changed as a result. The chopping process is thereby impaired.
For the chopping process to be precise and energy-efficient, not only is knife sharpness important, there must also be a certain distance between the shear bar and the cutting tool. If the distance is too great, a portion of the incoming material may not be cut completely, and greater cutting forces may be required. If the distance is too small, there is a risk in particular that the cutting blades and shear bar will touch each other, which can result in material damage and even cause material and/or machine elements to come loose, which is hazardous.
Therefore, there is a need to be able to precisely adjust the distance between the shear bar and the cutting tool, which poses a design challenge due to the high cutting forces that occur during operation.
From practical application it is known to couple a control unit to each of the diametrically opposed ends of the shear bar which comprises a counterblade bar extending approximately parallel to the rotation axis of the cutting cylinder. The two control units can be controlled using a control device, thereby enabling the clearance position of the shear bar relative to the cutting tool to be changed. Since the control units can be controlled independently of one another, the shear bar can be adjusted one side at a time.
It is imperative that the clearance be determined or at least estimated in order to set a clearance position of the shear bar that is adapted to the sharpened state of the cutting tool after sharpening. In practical application, this is carried out by moving the shear bar toward the rotating cutting tool until contact occurs, which can be detected by way of “knocking”, for instance, which can be detected in particular using “knock sensors” which are vibration sensors mounted on the shear bar.
To set a desired clearance between the shear bar and the cutting tool, it is known to move the shear bar—after the cutting tool has been sharpened—out of a position located at a distance from the cutting tool and move same toward the cutting tool. According to EP 0 291 216 B1, the control unit of a first side is activated first, in order to move the side of the shear bar assigned thereto toward the cutting tool until contact occurs between the rotating cutting tool and the shear bar. After contact occurs, the first side is retracted by a certain distance in order to attain a desired clearance. Once this first side has been adjusted, the diametrically opposed, second side of the shear bar is adjusted in the same manner, i.e. it is moved forward until contact occurs, and is then retracted by a desired distance.
Such an adjustment has disadvantages. Due to the above-mentioned high forces acting on the shear bar during operation, said shear bar is mounted in a rigid manner such that it cannot be adjusted without inducing a reaction. Adjusting the shear bar on one side therefore results in a load being placed on the shear bar itself and/or on the particular control unit. When the shear bar is moved forward in the manner described in EP 0 291 216 B1, there is a risk, therefore, that the shear bar will “jump” into the cutting tool due to various mechanical effects (sagging effects, rebounding, transition from stiction to kinetic friction). This can cause damage to the cutting tool and results in an inaccurate setting.
Since knock sensors used so far typically only detect contact of the shear bar with the cutting tool per se, and are unable to determine the location of the contact point, there is another risk, namely that contact detected by the sensor will be ascribed to the side of the control unit being activated at the moment, although the contact actually took place on the other side, due to loads and resulting uncontrolled return motions or other effects. As a result, the clearance position is set incorrectly.